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Two methods to predict the pushover response of a hybrid steel braced frame that features concentric and eccentric connections are presented. The proposed hybrid frame configuration is intended for cold-formed steel (CFS) building structures and plays a dual role by providing gravity and lateral load resistance. The hybrid system features CFS columns for resisting gravity loads, tension only CFS straps connected concentrically to hollow structural steel (HSS) chords for resisting lateral loads, and prestressing strands connected eccentrically to the same HSS chords for further enhancing lateral load capacity. The first pushover response prediction method employs a nonlinear finite element modeling protocol that features only beam and truss elements. This method is presented as an alternative to three-dimensional (3D) nonlinear finite element models, which require considerable modeling effort due to the multitude of the components included in the hybrid system, and the variety of interactions that would need to be defined. The second method includes closed form equations that allow the definition of the pushover curves using manual calculations and is appropriate for preliminary analysis. Formulations for predicting the initial in-plane system stiffness, and secondary stiffness are presented. Similarly, formulations for predicting the load to cause the first and second yield as well as ultimate lateral load capacity are provided. A closed form equation is presented to obtain the ultimate lateral displacement, which completes the definition of the pushover curve. The validation of the proposed pushover response prediction methods is conducted by first comparing responses from 3D nonlinear FEA to those obtained from the simplified FEA model. Similarly, predictions from the simplified FEA model are compared to those obtained from the closed form equations. Good agreements are noted in both cases. The influence of hybrid steel braced frame aspect ratio on system push over response is quantified. The contribution of each lateral load resisting element to lateral load capacity is presented as a function of aspect ratio. Finally, improvements in behavior and enhancements in lateral load capacity offered by the hybrid frame-wall compared to the traditional strapped wall system are demonstrated through monotonic pushover, cyclic pushover, and response history analysis. [ABSTRACT FROM AUTHOR]

Three desirable features of a seismic-resisting system's hysteresis are ductile behavior, consistent dissipation during loading cycles, and negligible residual displacements after earthquakes. A self-centering, pinching-free connector (PFC) was developed to attempt to meet these demands. The tension-only PFC uses a linear ratchet made from unified/metric screw threads to absorb the slack generated when a dissipator deforms/elongates monotonically. Nondestructive ratcheting tests were conducted to support the equations derived to predict the ratcheting behavior. Although the PFC can recenter unimpeded during tension (half) cycles, the ratcheting persisted on the compressive stroke during full tension-compression cycles and subsequently hindered its ability to recenter. Therefore, additional hook and ratchet stoppers were incorporated into the PFC to control the ratcheting and allow recentering from any position. This was verified in a preliminary test of a diagonally braced frame that demonstrated self-centering when unloaded. An incremental numerical procedure was able to predict the cyclic response of the frame satisfactorily from just the backbone curve of the PFC, which is mostly a reflection of the dissipator's backbone. This paper highlights an alternate means to self-centering dissipative systems through a linear ratchet that precludes the need for buckling restraints or substantial prestressing/poststressing. One implication is that very slender braces could be used in moderate-to-high seismicity regions because the pinching is no longer an issue and the dissipative potential is restored for monotonic dissipators. [ABSTRACT FROM AUTHOR]

This paper summarizes the results of a numerical simulation and subsequent variability analysis of the lateral load-resisting behavior of unbraced and chevron-braced glulam portal frames. Longitudinal tension/compression strengths of each glulam member were determined based on wood-size effect theory. The finite-element method (FEM) and an experimental study were carried out to determine the nonlinear mechanical behavior of glulam braces and bolted glulam beam-to-column connections. OpenSees "Pinching4" hysteresis models were adopted to model the mechanical behavior of both glulam braces and bolted beam-to-column connections. An FEM model of the glulam frames was developed to predict the lateral load-resisting hysteretic response of such frames. The stochastic finite-element method was used to calculate the frame capacity considering random distributions of connection and brace capacity. The FEM model presented can represent the nonlinear and hysteretic pinching behavior of an unbraced glulam frame whose behavior is dominated by splitting in the connection regions. Similarly, the strength softening and stiffness degradation of a chevron-braced glulam frame was also captured. Response surface method analysis was used to regress braced frame capacity from 200 analyses to a single set of capacity variables. The approach described in this paper demonstrates promise for optimizing the industrial-scale production of glulam portal frame structures. [ABSTRACT FROM AUTHOR]

• Novel framework combining OpenSees and VBA Excel Tool for efficient bracing and collapse assessment. • Practical code-based approach overcoming limitations of complex finite element methods. • Automatic plastic hinge display and UFC-based checks for quick identification of weaknesses. • Actionable recommendations for collapse prevention and improved structural analysis practices. Braced frames are among the most effective systems for resisting progressive collapse; however, determining the optimal bracing system remains challenging. Evaluating different bracing systems in this study was simplified using VBA programming tools and a flowchart that complied with the Unified Facilities Criteria (UFC)regulations (chapter 5). Applying control processes and automated VBA programming tools was beneficial for examining plastic hinges and guaranteeing adherence to the Unified Facilities Criteria (UFC)Design Strategies for Preventing Progressive Collapse in Building Structures.The study examined several types of braced frames, such as CBF and EBF, and found that the inverted V-braced systems (CBF and EBF) were the most efficient. They reduced the amount of vertical movement and dispersed the stresses on the remaining linked parts. Although there was a substantial vertical displacement, all beams and columns showed a decrease in overall force. The absence of a bracing system in the frame led to a violation of the regulatory criteria outlined in the control flowchart. The remaining structural systems exhibited exceptional performance. [ABSTRACT FROM AUTHOR]

Strongback-braced frames employ an essentially elastic truss, or strongback, that defines an elastic load path to redistribute seismic demands and mitigate the formation of story mechanisms. However, unlike the forces from traditional capacity design—which assumes that inelastic response limits the earthquake-induced forces—design forces in the strongback arise from a nonlinear first mode and near-elastic higher-mode response, because the strongback is designed to remain elastic in every mode. A design method using modal pushover analysis, which combines the response from pushover analyses in multiple modes, can estimate the magnitude and distribution of the force demands in the first and higher modes, including inelastic response. The existing modal pushover analysis procedure is simplified and applied to the design of the strongback in strongback-braced frames. Accounting for only the first mode of response resulted in estimates below the 16th percentile of force demands extracted from nonlinear dynamic analysis. However, a modal pushover approach using multiple modes resulted in improved estimates able to represent both the distribution and magnitude of the peak force demands from nonlinear dynamic analysis of eight- and four-story strongback-braced frames with buckling-restrained braces, while maintaining the conceptual simplicity of nonlinear static analysis procedures. [ABSTRACT FROM AUTHOR]

A novel self-centering device that employs disc springs as its kernel components is developed and experimentally verified in this study. The device is suitable for use in self-centering braced frames and is expected to provide a large initial stiffness, reliable self-centering capability, and satisfactory energy dissipation. The fundamental mechanical behavior of the new device is described first. The component detailing, working principle, and fabrication process are discussed in detail. This is followed by a series of tests on individual disc springs and friction plates to gain an in-depth understanding of the performance of these basic components. Subsequently, a full-scale device designed based on a prototype building is physically tested, and the reliability of the specimen under multiple earthquakes is further understood by carrying out repeated rounds of cyclic loading. Among other findings, it is observed that the proposed device has excellent self-centering capability with equivalent viscous damping (EVD) of up to 36%. The device can provide sufficient deformability, corresponding to an available interstory drift of at least 4%. The device is capable of withstanding multiple rounds of loading with no degradation, highlighting its superiority for use against sequential strong earthquakes with no need to replace/repair. The analytical expressions are validated through comparisons against the test results, and a parametric study is then conducted to examine the effects of some key design factors on the device behavior. Based on the experimental and analytical studies, some practical design recommendations are finally given. [ABSTRACT FROM AUTHOR]

This paper deals with a Continuous Stiffness Degradation (CSD) version of advanced analysis of braced steel framing. It is based on the gradual stiffness degradation concept of frame and truss members. A novelty of the approach presented herein is related to the introduction of the bracing member response in the whole range of its behaviour in tension and compression, including the post-limit range. The validation of the proposed advanced analysis is performed for braced framework with rolled angle section braces. The validation of the brace force-deformation model has been presented in the author’s earlier publication. The basis for the presented CSD advanced analysis is briefly summarized and its difference with regard to the Refined Plastic Hinge (RPH) version of advanced analysis is emphasized. Experimental investigations dealing with tests on portal braced sub-frame specimens are referred to briefly. Results of the experimental investigations are presented in the form of a frame global response and they are used for the validation of the developed computational model.

This paper is entirely devoted to practical aspects of direct design and assessment of safety and serviceability of steel planar framework using advanced analysis. The development of advanced analysis has been driven by a desire for a more accurate representation of the behaviour of planar framework by considering the beam and spring numerical modelling technique together with plasticity and geometrically nonlinear effects as well as structural imperfections accounted for. The validated 2D version of CSD advanced analysis developed by the author is used in this paper for its practical application towards the resistance and serviceability assessment of existing simple construction framework. This steel braced frame was a subject of technical expertise. The same structure geometry but with different joint detailing is then considered to show how the effect of joint properties may affect the braced frame performance. Results of investigations are presented in the form of frame global response at both the ultimate limit state and the serviceability limit state, and also in the form of member local responses. Conclusions with regard to general design and assessment practice are drawn.

Abstract A method is presented for optimal placement of braces of plane frames using machine learning. The frame is subjected to static horizontal loads representing seismic loads. We consider the process of seismic retrofit by attaching braces. Therefore, the maximum value of additional stresses in the existing beams and columns and the maximum interstory drift angle are incorporated in the optimization problem. Characteristics of approximate optimal solutions and nonoptimal solutions are extracted using machine learning based on support vector machine and binary decision tree. Convolution and pooling are used for defining the features characterizing the solutions while reducing the number of variables. Optimization is carried out using a heuristic algorithm called simulated annealing based on local search. It is shown in the numerical examples that the computational cost is successfully reduced by avoiding costly structural analysis for a solution judged by machine learning as nonoptimal, and the important features in approximate optimal and nonoptimal solutions are identified.

Application of bracings to increase the lateral stiffness of building structures is a technique of seismic improvement that engineers frequently have recourse to. Accordingly, investigating the role of bracings in concrete structures along with the development of seismic fragility curves are of overriding concern to civil engineers. In this research, an ordinary RC building, designed according to the 1st edition of Iranian seismic code, was selected for examination. According to FEMA 356 code, this building is considered to be vulnerable. To improve the seismic performance of this building, 3 different types of bracings, which are Concentrically Braced Frames, Eccentrically Braced Frames and Buckling Restrained Frames were employed, and each bracing element was distributed in 3 different locations in the building. The researchers developed fragility curves and utilized 30 earthquake records on the Peak Ground Acceleration seismic intensity scale to carry out a time history analysis. Tow damage scale, including Inter-Story Drifts and Plastic Axial Deformation were also used. The numerical results obtained from this investigation confirm that Plastic Axial Deformation is more reliable than conventional approaches in developing fragility curves for retrofitted frames. In lieu of what is proposed, the researchers selected the suitable damage scale and developed and compared log-normal distribution of fragility curves first for the original and then for the retrofitted building.

Although brace-type hysteretic dampers have been widely adopted to mitigate structural damage under severe earthquakes, their performance was often limited by premature rupture of the welded corner gusset connection or its surrounding framing members due to additional frame action. Such a frame-gusset interaction was found more detrimental for buckling-restrained braced frames (BRBFs). A sliding corner gusset connection, which is connected to beam and column flanges by bolted end plates, but allows sliding deformations at the frame-gusset interfaces via employment of butyl rubber layers, is proposed to minimize such an interaction. Cyclic tests of three steel BRBF subassemblages, two with the proposed sliding configuration and another with the traditional welded one, were conducted to verify effectiveness of the proposed connection. Test results show that significant plastic damages were observed on the welded gusset connection and its surrounding beam. Seismic performance of this specimen was limited by significant out-of-plane and local buckling of the beam prior to brace rupture. Such an undesirable failure could be avoided by the proposed connection, in which the specimen with beam flange reinforcing plates exhibited satisfactory performance up to 4% drift, followed by additional 3% drift with 11 more cycles until brace rupture. The proposed connection is effective in reducing the seismic shear and flexural responses on the framing members, as well as the stress responses at the gusset interfaces. Structural behavior of the two types of gusset connection is compared and future research needs for design of these connections are provided. [ABSTRACT FROM AUTHOR]

A method is presented for optimal placement of braces of plane frames using machine learning. The frame is subjected to static horizontal loads representing seismic loads. We consider the process of seismic retrofit by attaching braces. Therefore, the maximum value of additional stresses in the existing beams and columns and the maximum interstory drift angle are incorporated in the optimization problem. Characteristics of approximate optimal solutions and nonoptimal solutions are extracted using machine learning based on support vector machine and binary decision tree. Convolution and pooling are used for defining the features characterizing the solutions while reducing the number of variables. Optimization is carried out using a heuristic algorithm called simulated annealing based on local search. It is shown in the numerical examples that the computational cost is successfully reduced by avoiding costly structural analysis for a solution judged by machine learning as nonoptimal, and the important features in approximate optimal and nonoptimal solutions are identified. Machine learning is applied to reduce the computational cost for optimization of brace locations of building frames. The properties of approximate optimal solutions and non‐optimal solutions are identified by binary decision tree and support vector machine. [ABSTRACT FROM AUTHOR]

This article presents an analytical study of the seismic collapse performance of seismically isolated buildings and comparable non-isolated buildings. The study is based on archetypical 6-story perimeter frame seismically isolated buildings designed with special concentrically braced frames (SCBF), ordinary concentrically braced frames (OCBF) and special moment resisting frames (SMF) for a location in California using the minimum criteria of ASCE/SEI 7-10 and ASCE/SEI 7-16 and also using a number of enhanced designs. The isolation system consists of triple Friction Pendulum (FP) isolators with stiffening behavior at large displacement. Additionally, double concave sliding isolators are considered and designed per minimum criteria of ASCE/SEI 7 and without a displacement restrainer, a practice permitted by the standards. Non-isolated structures, also with braced and moment frame configurations, are designed using the minimum criteria of ASCE/SEI 7 and studied. The study concludes that seismically isolated buildings designed by the minimum criteria of ASCE/SEI 7 of either 2010 or 2016 may have unacceptable probability of collapse in the Risk-Targeted Maximum Considered Earthquake (MCE R ). The probability of collapse in the MCE R becomes acceptable when they are designed with enhanced criteria of R I =1.0 and with isolators having a displacement capacity at initiation of stiffening equal to 1.5 times the demand in the MCE R . It is also observed that designs that meet the minimum criteria of ASCE/SEI 7 of either 2010 or 2016 and without any displacement restrainer have unacceptably high probabilities of collapse. [ABSTRACT FROM AUTHOR]

Structures designed in accordance with even the most modern buildings codes are expected to sustain damage during a severe earthquake; however; these structures are expected to protect the lives of the occupants. Damage to the structure can require expensive repairs; significant business downtime; and in some cases building demolition. If damage occurs to many structures within a city or region; the regional and national economy may be severely disrupted. To address these shortcomings with current seismic lateral force resisting systems and to work towards more resilient; sustainable cities; a new class of seismic lateral force resisting systems that sustains little or no damage under severe earthquakes has been developed. These new seismic lateral force resisting systems reduce or prevent structural damage to nonreplaceable structural elements by softening the structural response elastically through gap opening mechanisms. To dissipate seismic energy; friction elements or replaceable yielding energy dissipation elements are also included. Post-tensioning is often used as a part of these systems to return the structure to a plumb; upright position (self-center) after the earthquake has passed. This paper summarizes the state-of-the art for self-centering seismic lateral force resisting systems and outlines current research challenges for these systems.

Double-web angle connection is one of the most rudimentary connections in simple structural systems such as braced frame system. It is essentially presumed in conventional designs that double-web angle connection behaves as a hinge connection. However, in braced frames, due to existence of braces in some bays, in specified locations where gusset plates of brace are placed with beam-to-column connection in one joint, this assumption may not be accurate. This is due to the restraining of the beam from rotation by gusset plates that are placed either on the top and bottom of the beam or only on one side. In such cases, the simple beam-to-column connection may be transformed into a semi-hinge or fixed connection. In this paper, double-web angle connection is investigated in the mentioned locations by using the FEM method along with calculating moment rotation behavior of connection and, subsequently, type and rigidity of the connection. Furthermore, an analytical model is proposed to predict the characteristics of the doubleweb angle connection in the view of the relevant case. [ABSTRACT FROM AUTHOR]

A three-segment steel brace has been developed and investigated by means of numerical and experimental studies. The objective of the development was to develop a brace member that exhibits stable and symmetrical cyclic response under cyclic loading. The concept was conceived by extending a conventional elastic buckling of a column with variable sections to include post-buckling deformation. The concept was first examined using FEM-based simulations, and tested experimentally with an ensemble of small-scale brace specimens under cyclic loads. Seismic response of CBFs with conventional buckling braces and the three-segment braces were compared and results are discussed in terms of drift, brace and beam ductility demands. The results indicate that the tested three-segment braces specimens were capable of exhibiting stable and symmetrical hysteretic response, as well as dissipating a greater amount of energy compared to conventional buckling braces. Further, the dynamic analyses results point out that substituting the conventional buckling braces with the three-segment braces substantially mitigates the seismic demand on the braced frames. [ABSTRACT FROM AUTHOR]

The self-centering energy-dissipative (SCED) brace is a novel bracing element that can substantially reduce the residual deformation and enhance the reparability of structures. In this paper, nonlinear dynamic analyses have been conducted on a 4- and a 12-story steel-braced frame with SCED braces to study the effect of four important design parameters on the seismic performance of the SCED frames and recommendations are given for selection of the parameters. The parameters considered include the response modification coefficient , the stiffness ratio of the brace , the strength ratio of the brace , and the fuse activation story drift . The relationship between the residual story drift and the peak story drift of the SCED frames is obtained based on these statistics. Finally, based on the equivalent linearization theory, a direct displacement-based design method applicable to the SCED frames, regarding both the peak story drift and residual story drift as the design objectives, is proposed. [ABSTRACT FROM AUTHOR]

In seismically active regions, many old low- to mid-rise reinforced concrete (RC) buildings are in use that have poor reinforcement details and suffer from material deterioration. Because these buildings are vulnerable to earthquakes, they represent a threat to human lives and economy. To impart such a building with satisfactory seismic performance, a friction damping system can be used, which consists of dampers and a braced frame. In this study, a method for the design of friction damping systems is proposed for the seismic retrofit of old low- to mid-rise regular reinforced concrete (RC) buildings. The proposed method is verified using a six-story RC building designed considering only gravity loads. [ABSTRACT FROM AUTHOR]

A shape memory alloy based articulated quadrilateral bracing system is developed and experimentally tested for seismic resisting applications. The articulated quadrilateral arrangement provides a scalable, reconfigurable, convenient means of combining nickel-titanium (NiTi) wires and energy dissipating elements. This configuration creates a system with an adjustable amount of recentering and damping, which could potentially be used in a wide variety of new and existing buildings. For these prototype tests, NiTi wire bundles were combined with long C-shaped dampers to create a system with a good balance of recentering and energy dissipation. The system was subjected to cyclic loading to assess the behavior. The system maintained strength, ductility, and recentering after being cycled to 2% drift, which is a typical maximum in structural systems if non-structural elements are to be preserved. An analytical case study demonstrated that shape memory alloy systems tend to distribute the deformation more evenly over the height of the structure compared to traditional systems, which is a desirable seismic performance characteristic. It is envisioned that, by using the same basic bracing setup, a wide range of force-deformation responses can be at an engineer's disposal. [ABSTRACT FROM AUTHOR]

• Impacts of the design utilization ratio on seismic response of different brace configurations are investigated. • Four bracing configurations designed according to the National Building Code of Canada and Canadian Standard CSA S16, with two design utilization ratios are considered. • Results confirm that use of a brace design with high utilization ratio can reduce material use by about 50% while maintaining the unique characteristics. • FEMA P-58 residual displacement equation predicts displacements accurately for some braced frame types with high utilization ratios, whereas it overestimates the same for others. Concentrically braced frames are common and effective systems for resisting earthquake forces in low and high-rise buildings. While various brace configurations can improve seismic performance, steel yielding causes residual drifts, which complicate or render the repair of damaged buildings irreparable. Minimizing seismic residual drifts is, therefore, imperative. The Superelastic Shape Memory Alloys (SE-SMAs) are superelastic materials capable of experiencing large plastic deformations and regaining their original shape upon unloading. Their use in steel structures reduces residual deformations associated with seismic events and will facilitate post-seismic retrofitting. The impacts of the utilization design ratio (UDR) on the seismic response of different brace configurations are investigated using two utilization design ratios (UDR1 and UDR2). The results show that using the UDR2 reduces the used SE-SMA material while maintaining the unique characteristics of SE-SMA material. Further, the FEMA P-58 equation accurately predicts residual displacements for I-VBF and M−XBF when braces are designed using UDR2 but overestimates residual displacements for VBF and XBF when the same UDR2 is used. [ABSTRACT FROM AUTHOR]

• A novel seismic design method is proposed for hybrid braced frames with SCBs and FVDBs. • The constant-ductility spectra are constructed for damped flag-shaped hysteresis. • The design method is robust for a wide range of viscous damping ratios. • The FVDBs with viscous damping ratio of 5% could effectively reduce floor accelerations. Combining self-centering braces (SCBs) and fluid viscous damping braces (FVDBs) in parallel emerges as a promising seismic-resistant strategy, because it has the potential of simultaneously controlling peak deformation, peak acceleration, peak base shear and nearly eliminating residual deformation. However, the corresponding seismic design method is still under development. To this end, this paper extended the performance-based plastic design (PBPD) method to hybrid braced frames (HBFs) equipped with SCBs and FVDBs. The PBPD method selected target drift and yield mechanism at the very beginning of the design procedure, and then it derived the design base shear using energy equivalent concept. The key step was to obtain the constant-ductility spectra of the equivalent single-degree-of-freedom systems through nonlinear time history analysis (NLTHA). The regression functions of the spectra were then incorporated with the PBPD procedure. A six-story steel frame was selected for demonstrating the design method. A total of 4 HBFs were designed by defining 4 levels of viscous damping ratio (ξ v) supplemented by FVDBs. The seismic responses of the designed HBFs were examined by subjecting them to 20 earthquake ground motions. The NLTHA results indicated that the designed HBFs can well satisfy the performance targets. The design method was robust, although the ξ v values were varied in a wide range. The design method may also shed light to the other types of hybrid systems with displacement- and velocity- dependent damping braces. [ABSTRACT FROM AUTHOR]

In seismic design, structural irregularity has been found to have a significant influence on structural response. The impact of structural irregularity on the global response of steel frame structures subjected to blast loading has not been examined. In the paper, six seismically designed steel framed structures are considered: moment resisting frames (MRF), concentrically braced frames (CBF) and eccentrically braced frames (EBF) each with geometric irregularity in the plan and with a geometric irregularity in the elevation. The blast loads are assumed to be unconfined, free air burst detonated 15 ft from one of the center columns. The structures are modeled and analyzed using the Applied Element Method, which allows the structure to be examined during and through structural failure. A plastic hinge analysis is performed as well as a comparative analysis observing roof deflection and acceleration to determine the effect of geometric irregularity under extreme blast loading conditions. Two different blast locations are examined. Conclusions of this research are a concentrically braced frame provides somewhat of a higher level of resistance to blast loading for irregular structures and geometric irregularity has an impact on the response of a structure subjected to blast loading.

This paper presents the results of experimental studies performed on three 1/3-scale steel building frames for comparative assessment of the cyclic behavior of a Chevron frame equipped with a newly-developed damper, THDF (Torsional Hysteretic Damper for Frames) in relation to a Chevron special concentrically braced frame (SCBF) and an eccentrically braced frame with a vertical H-link. THDF is a damper with a displacement-dependent post-elastic stiffness, developed for Chevron frames. First, the SCBF was designed as a full-scale frame according to the requirements of AISC 360–16 and AISC 341–16, and scaled down to 1/3-scale according to similitude requirements due to limitations of the testing facilities. The other two frames are designed as scaled frames by adjusting their braces and energy dissipation elements so that the frames have similar levels of yield force. The frames are subjected to quasi-static cyclic tests of increasing amplitude until failure. In the case of SCBF and H-link frames, the force levels observed in the tests were higher than predicted due to oversight in the fabrication of the test specimens, which may not be the case in practice. In the case of the H-link frame, this led to early failure of the connection before the full plasticization of H-link. SCBF was tested up to low-cycle fatigue failure of both braces. The THDF-equipped frame showed stable force-displacement loops with little variation in force levels and a better distribution of energy among the stories. • The analytical force-deformation hysteresis equations of a newly developed hysteretic damper for uniform energy dissipation along the height of braced frames is verified experimentally. • The seismic performance of a braced frame equipped with the newly developed damper is experimentally studied in comparison to a special concentrically braced frame and eccentrically braced frame. • The ability of the newly developed damper to ensure uniform energy dissipation along the building height is demonstrated via comparative experimental studies. • The advantages of the damper equipped frame with respect to the conventional chevron braced frames are outlined. [ABSTRACT FROM AUTHOR]

The first-order elastic analysis cannot capture the second-order effects owing to the change in structural geometry, such as P-Δ and P-δ effect, which can cause the second-order moment in order to deteriorate the stiffness of a structure. Unfortunately, the first-order elastic analysis is prevalent in the design office and the current practical engineers have not yet well equipped for manipulating the advanced analysis for design purpose. To this end, AS4100 stipulates the design calculation of moment amplification factor for the braced and sway member continuous in a framed structure in Section 4 of the method of structural analysis as a system approach; specifically for an axially compressive loaded column in either a braced or sway frame. However, in this study, it is shown that the moment amplification factors as a system approach is not as effective and sophisticated as the member design approach. In this regard, this paper reviews the moment amplification factor for the second-order effects on a rectangular portal frame with recourse to the first-order elastic analysis, and finally discusses an issue between the second-order moment amplification factor and the member buckling design, which can facilitate the design section of the system approach in AS4100 in alignment with the advanced analy"?>sis for the future system design approach. [ABSTRACT FROM AUTHOR]

Column calculation on frame system is a long and iterative process. This program is used to calculate column on general aspects, these aspects are slender, biaxial, braced frame and sway frame. This program uses Borland Delphi 7.0 language. Data input consists of material data (fy, f�c), load data (Pu, M1bx, M2bx, M2sx, M1by, M2byand M2sy), column data (b, h and L) and beam data(bb, hband Lb). The gained result is the table that contains output data of calculation, that is slender limit, k.Lu/r, ψA, ψB, k, δB, δS, Mc, As, As/Ag, β, Pn pl, Pn ada, Mn pl, Mn adafor axe x and axe y. For validation, output of calculation can be compared between manual and program calculation. The results of comparison are the biggest error percentage 0,0054% and smallest error percentage 0% (not difference). This is because in manual calculation there is always rounding every step, while in the computer calculation rounding is done at the end of process. Performance of the program is proper and satisfying to be used in short time and accurate.

In a conventional suspended zipper braced frame (SZBF), the required strength of zipper columns and top story braces increases rapidly with the number of stories, resulting in unacceptable cross sections for these members. To overcome these drawbacks, a new modified suspended zipper braced frame (RZBF) is proposed in this paper. Compared with SZBF, the two central ideas of RZBF are that the unbalanced vertical forces at each story do not reach the maximum values simultaneously, and that the braced beams can transfer part of the unbalanced vertical forces during earthquakes. In order to understand better the seismic performance and design advantages of RZBF, nonlinear time history analyses were conducted on 3, 6, 10, 15, and 18-story RZBF and SZBF models. Comparison of the results obtained demonstrates the efficiency and viability of RZBF. Moreover, it is shown that the RZBF saves more steel material as the number of stories increases. [ABSTRACT FROM AUTHOR]

In seismic design, structural irregularity has been found to have a significant influence on structural response. The impact of structural irregularity on the global response of steel frame structures subjected to blast loading has not been examined. In the paper, six seismically designed steel framed structures are considered: moment resisting frames (MRF), concentrically braced frames (CBF) and eccentrically braced frames (EBF) each with geometric irregularity in the plan and with a geometric irregularity in the elevation. The blast loads are assumed to be unconfined, free air burst detonated 15 ft from one of the center columns. The structures are modeled and analyzed using the Applied Element Method, which allows the structure to be examined during and through structural failure. A plastic hinge analysis is performed as well as a comparative analysis observing roof deflection and acceleration to determine the effect of geometric irregularity under extreme blast loading conditions. Two different blast locations are examined. Conclusions of this research are a concentrically braced frame provides somewhat of a higher level of resistance to blast loading for irregular structures and geometric irregularity has an impact on the response of a structure subjected to blast loading. [ABSTRACT FROM AUTHOR]